The main function of concrete reinforcement support chairs, commonly referred to as chairs, is to hold tension cables and reinforcement bars/rods (“rebar”) within concrete structures, such as roadways, highways, runways, floors, building walls, retaining walls, foundations and flat work. Wire ties have long been used to connect the chairs to the cables or rebar. Extra labor time and expense is necessary to install the ties by hand. In addition, chairs are often overlooked or skipped during the tying process.
More recently, chairs have been developed that do not require the use of separate ties, but such chairs are securely affixed to the cables or rebar. As a result, these chairs are susceptible to movement when the cables or rebar are being laid or tensioned, or when the concrete is poured. The resulting movement can affect the structural integrity of the concrete structure. Moreover, these chairs do not allow for opening or reclosing the fasteners without great difficulty or a high probability of damage to the chair. As a result, such chairs do not allow for relocation or adjustment. Moreover, some of these chairs also have multiple parts that increase the complexity and cost of the installation.
Another problem occurs when liquid concrete flows into a form. The force of the concrete displaces plastic chair supports out of position to float freely within the concrete matrix, or causes them to rotate around and upward on the cable, leaving them sticking out of the finished concrete. When the flow of concrete knocks over chairs which are tied to cables, the cables are stretched and pushed out of the engineered pattern. Yet another problem occurs when moisture barriers of polyurethane, or similar materials, are installed beneath concrete. In such installations, there is a tendency for the sheets of barrier material to blowout of place in windy conditions. This can also cause movement or rotation of the chairs. Additionally, air pockets occur between the ground and the barrier material when concrete is poured into place, creating thin, weakened areas of concrete which cause potential structural problems. Although some chairs have been designed with small projections on the feet/base to increase friction, such projections are not long enough to adequately solve these problems. Moreover, the installer must select chairs with projections or without projections—the chairs are not configurable in the field.
As a result, there is a need for a chair that is inexpensive to manufacture, easy to install and allows for longitudinal movement of the cables or bars.